Time- and spectrally resolved singlet oxygen phosphorescence detection-discriminating disturbance signals

Singlet oxygen is well known as the main mediator of photodynamic therapy. Therefore, great efforts are being made to detect singlet oxygen in many different biological environments. The most promising method is the time-resolved luminescence detection via its very weak nearinfrared phosphorescence. However, in many biological environments these time-resolved measurements suffer from signal artifacts at short times (within the first 2 mu s) after the excitation pulse. Neither the origin nor the kinetics of these disturbance signals have yet been successfully elucidated. Up to now, no way for eliminating them has been developed, be it mathematical or experimental. This work reports about a method for discrimination of the singlet oxygen phosphorescence from a disturbed signal by spectrally resolved measurements. We use a tiltable interference filter as an experimentally efficient and comparably cheap method to conduct highly sensitive time-and spectrally resolved luminescence measurements, inherently suitable for the future application in biological systems. We use Rose Bengal in water as an example system. It generates singlet oxygen at high quantum yield and shows additional luminescence emissions. The complex luminescence of Rose Bengal is treated as the disturbance signal. The isolation of the singlet oxygen phosphorescence by a fitting algorithm is demonstrated.